This invention concerns closed cycle cooling systems and more particularly those of miniature Stirling type. As is known, such systems include as basic parts thereof two major components: the compressor unit and the expansion unit. One group of such coolers is of the so called "split type" wherein compressor and expander unit are strictly separate from one another and are interconnected by a gas conduit or conduits. The second group is of the so called "integral type" wherein compressor and expander are mechanically coupled and activated by the same crankshaft.
In a cooler belonging to the Stirling thermodynamic cycle kind, there is provided a sealed casing containing the compressor unit only in the split type and the compressor and expander in the Integral type cooler. The cooler includes a crankshaft driven by an electromotor. A piston actuated by the said shaft creates the required pressure pulses and the columetric reciprocal change in the expander in the integral type cooler.
In the Stirling type of cooler, the electromotor is conventionally located within the gaseous atmosphere, i.e., the gas used in operating the cooler. Obviously, specially designed motors have to be employed.
Now, as is known, one of the reasons for faulty performance of the cooler is contamination of the gas caused to a large extent by residual gas remaining in the system after precluding or due to evaporation of high vapour pressure materials in the interior of the cooler. So, e.g. organic varnishes used for insulating rotor or stator windings of the motor are a main source of gas contamination. The motor, being located within the working gaseous atmosphere, presents certain problems of maintenance, since in order to reach it, the region where the gas is contained in has to be open to the air.
In order to do away with the above disadvantageous, I have suggested in my U.S. Pat. No. 4,558,570 to use an ordinary - not specially designed - electromotor and to locate it at the exterior of the gas enclosing housing and to provide a magnetic torque-coupler for the rotational transfer of drive from the electromotor to the compressor crankshaft located within a casing in relation to which the motor is exteriorily located.